1. Field of the Invention
This invention relates to a catheter for use in vascular embolectomy.
2. Description of the Prior Art
As a common therapy for cerebral aneurysm, a method which comprises craniotomy and clipping the neck of aneurysm has existed to date. Since this method is highly susceptible of surgical invasion, the possibility of this method entailing a complication is undeniable. For the purpose of improving the results of therapy for morbidities in the cerebral blood vessels such as large aneurysms which render surgical operations impossible or difficult and alleviating the physical, spiritual, and economic burdens on the part of patients, the intravascular surgical therapy which uses a vascular catheter without inducing a surgical invasion has been gaining in impetus (Katsuya Goto, "Neurosurgeons," 9, 229-239, 1990).
The intravascular surgical therapy effects the cure of a morbidity in the cerebral blood vessel, for example, by inserting a miniature catheter extremely selectively into the affected part of the cerebral artery and occluding a cerebral aneurysm with an embolic material which is introduced by the catheter.
The cerebral blood vessel lacks the external elastic membrane and possesses only a thin vascular wall as compared with other parts of the brain and, therefore, offers weak resistance to the lateral pressure of bloodstream. Inside the cranium, the blood vessels run intricately. Particularly in a patient of hypertension, the ramified parts of such blood vessels are liable to sustain an injury from the pressure exerted thereon. The statistics on anatomical examinations indicate that the cerebral aneurysms are aneurysms occurring in the artery system in one out of 100 adults and have a wide shape distribution approximately ranging from 1 mm to more than 20 mm in diameter and that the cites of genesis are widely varied over cerebral arteries with the Willis ring as the center. When the cerebral aneurysms are fractured, they cause such serious cerebrovascular injuries as subarachnoid hemorrhage and intracerebral hemorrhage. When they grow gigantically in size, they induce the compression symptom of the cerebral nerves. Arteriovenous malformations abound most in all the malformations of the cerebral blood vessels and are widely known. They are an aggregate of zigzagging and dilated influent and effluent blood vessels and arteriovenously inosculated blood vessels intervening therebetween. Clinically, they form an important cause for intracerebral hemorrhage, epilepsy, and progressive nervous breakdown which reach crisis in relatively young patients.
The embolectomy cures such a morbid alteration in the cerebral artery as mentioned above by occluding the affected part with an occluding substance thereby blocking the bloodstream in the affected part and solidifying the site of disease. The solidified site of disease, when necessary, is excised.
The cure of cerebral arteriovenous deformations has now reached the point where the embolectomy plays the main role in therapy (Goto K. et al., Neuro radiology, 33, [Suppl] 193-194, 1991). This situation is expected to prevail in the cure of cerebral aneurysms in the near future (Katsuya Goto, "Walks of Medicine," 153; 635, 1990). The trend has encouraged scientists to search various substances for embolic materials.
Heretofore, cyano-acrylate type materials have been in popular use as liquids for occluding sites of morbid alteration in the blood vessels (J. Biomed. Mater. Res., 17, 167-177 (1983)M. C. Harpers et al.).
Recently, it has been proposed to adopt the dimethyl sulfoxide (DMSO) solution of an ethylene-vinyl alcohol copolymer (a commercial product marketed under trademark designation of "Eval") as an embolic material and allow the DMSO to be diffused in the blood and the Eval to precipitate and occlude the blood vessel (Medical Tribune, Oct. 26, 1989, pp. 46 and 47).
Meanwhile, the method which comprises inserting a catheter accompanied by a separable balloon into an aneurysm, inflating the balloon thereat and occluding the aneurysm, and allowing the inflated balloon to indwell inside the aneurysm has found popular acceptance (Journal of Neurosurgery, 41, 125-145 (1974), F. A. Serbinenko).
Other means heretofore adopted for the therapy in question include metallic coils (minicoils), polyvinyl alcohol (PVA) sponges, alcohols, and sutures which have been selectively used to suit particular objects of therapy.
The conventional cyano-acrylate type embolic material is injected into the site of aneurysm with difficulty because it quickly undergoes curing polymerization in the blood vessel. For the purpose of preventing the catheter from being stuck to the interior of the cerebral blood vessel with this material which is capable of manifesting a powerful adhesive action, the catheter inserted into the blood vessel must be extracted at a stroke as soon as the injection of the material into the site of disease is completed. Thus, the material allows no easy handling. The injection cannot be repeated even when the occlusion obtained at all turns out to be imperfect. This embolic material is further at a disadvantage in inflicting a grave stimulus to the wall of the blood vessel and inducing a strong inflammatory reaction.
In the system using Eval dissolved in the DMSO solvent, part of the solvent remains persistently in the central part of the mass of Eval which has been precipitated on contact with the bloodstream. When this system is used in the treatment of the aneurysm by the embolectomy, the disadvantage arises that the part of the material which has leaked into the blood vessel from the exit side of the aneurysm adheres to the branched part of the blood vessel along the path of the bloodstream.
No safety has been established yet for the DMSO as the solvent [Hiroo Iwata et al., Collection of Scripts for Presentation at the 11th General Meeting of Japan Biomaterial Society (1989), 68, II-22]. Further, the solvent exerts an injury to utensils made of resinous materials. When the system is used in the manner of directly injecting the solution into the site of aneurysm through the medium of a catheter as described above, it is not perfectly safe to regard the solvent optimum.
More often than not, the separable balloon is adopted in the treatment of the aneurysm by the embolectomy. When the balloon is used at all, since the reaction between the balloon and the inner wall of the aneurysm is weak, the possibility that the inflated balloon will not thoroughly fill out the empty cavity inside the aneurysm and the disease will recur if even a small portion of the empty cavity remains unfilled is high. An attempt to fill up amply the inner cavity of the aneurysm by inflating the balloon to the largest possible volume results in increasing the inner pressure of the balloon possibly to the extent of altering the shape of the aneurysm and rupturing the aneurysm. The separation of the inflated balloon from the catheter requires application of tractive force to the catheter and exalts the possibility of fracturing the aneurysm.
At the present time, perfect isolation of the site of aneurysm is difficult to achieve by the method which resorts to the use of the separable balloon or a minicoil. Thus, the method of proximal occlusion which comprises partially occluding the parental artery is adopted more often than not [Akira Takahashi, "Walks of Medicine," 154, (7), 432, (1990)]. This method, however, exposes the brain to the possibility of hindering the bloodstream because it requires to sacrifice the parental artery. The method which resorts to simultaneous use of a separable balloon and minicoils has been proposed for the treatment of a gigantic aneurysm by the embolectomy (Katsuya Goto, Collection of Excerpts for Presentation at the Study Meeting of Japan Angiography IVR, 1991). This method requires to use many expensive minicoils, consumes much time, and lacks in the effect of reducing pressure. In other words, it is at a disadvantage in offering low packing density and encountering difficulty in decreasing the inner pressure of the aneurysm immediately after the balloon has been indwelt.
Besides, such materials as PVA granules, alcohols, and sutures entail many therapeutic problems such as difficult handling and insufficient effect of treatment.
It is, therefore, a primary object of this invention to provide for an embolectomy catheter which permits the embolectomy to be performed safely and infallibly on an aneurysm.
A further object of this invention is to provide an embolectomy catheter which allows formation of an embolic material capable of restraining diffusion of minute fragments thereof within the blood vessel.
Another object of this invention is to provide an embolectomy grade catheter which permits formation of a filamentous embolic material.
Still another object of this invention is to provide an embolectomy catheter which permits formation of an embolic material aimed at a morbid alteration of the blood vessel and adapted to restrain a secondary reaction, if any, of a solvent used in the material to the fullest possible extent.
Yet another object of this invention is to provide an embolectomy catheter which offers a high filling density and permits a reduction in the inner blood pressure of aneurysm immediately after the embolic material has been introduced.
Throughout this specification, the term "spinning means" or the like is used generally to define any type of device for producing a filamentous material, such as an extruder, a nozzle, a device to impart shear stress to the extruded material to "spin" the material, etc.